Hi Everyone, There have been a number of questions about my newest project (5751 SRPP / EL84 (6BQ5) Push-Pull Tube Amp) that are showing up in the Odd Block Thread so I thought I would start a new topic. For those of you who have not seen the amp, please look at the web site for it. This is a smaller amp similar in design to the Odd Blocks. It is stereo and has more gain so it can be used with many different sources. The actual performance surprised me, as I wanted it to be a modest cost project and figured that the sound would not be quite as good as the bigger amps. Not so. It can't compete with the KT77s and KT88s, but it is awfully nice. Except for power output it is much the same in all areas except below 30HZ. At sub 30 frequencies the distortion is higher than the big guys. It isn't audible on my Martin Logan Vistas, but they roll off at about that range anyhow. Excellent response (way past 20K), low distortion, very quiet (I won't put up with hum and noise in my projects) great sound stage and detail. All this was quite a surprise. And yes (no sales pitch and trying not to be commercial here) kits are in the works, through OddWatt Audio. All quality parts and everything needed to build one. Price is not yet fixed but will be reasonable. As always I will support both diy and kit questions equally. Build away, this is a fairly simple amp and will deliver a high quality sound. It can be used as a main system amp and is best used with full range (30hz to 20Khz) systems with better than 90 db/watt sensitivity. In smaller rooms it is fine with ones down to 85db/w. The prototype is going to reside in my office and drive some Klipsch KG4s.

Good listeningBruce

Author:

rparsh [ 13 Mar 2010, 10:00 ]

Post subject:

Re: PoddWatt EL84 Push-Pull Stereo Tube Amp - Support Thread

Hi Bruce, I hooked up a pair of Polk Audio TSi100 big bookshelf speakers (4 ohm) to my Poddwatt (see Poddwatt EL84 Push-Pull, 575 input Tube Amp thread) and a cheap Sony Walkman CD / FM radio combo to drive it and it sounds wonderful first time ever used. I have EH EL84 tubes and Sovtek 5751 tubes. The SRRP voltage is 220 volts and the B+ to the output trans is 230 volts. There is 80 volts to the SRRP filaments and exactly 12.1 volts running the heaters. Every part is exactly as specified in the schematic. I wish the Edcor output trannies were enclosed instead of open like they are with external solder tabs. Guess I will put some silicone sealant on all those exposed HV terminals before I get zapped! I used a regular KT 88 type Power transformer with 250ma output. The CCS on both channels is 41.1mv. The Tube Amp Doctor EL84s were only off by 2mv from channel to channel. I will install my EH output tubes shortly. I just wanted to be sure everything was OK before I put in the EH EL84s. Now on to the next project. I think I will build a two tube 832A amp since I have 10 of those tubes. Its amazing how many tubes you can accumulate over a short time. I will have to put up some shelves for all these amplifiers. I think the next time I use a ALPS dual volume control I will make a small pc board so I can spread out the terminals a little further. Do they not make them with solder lugs instead of pc pins? Also, where do you get your Russian KY049 caps? I would like to try a couple of those. I used 2 Auricaps in the Poddwatt. I also used 4 Solen .33 caps in my two KT88 Oddwatt amps. They sound great also. Thanks, Robert Parsh

Author:

gofar99 [ 13 Mar 2010, 20:55 ]

Post subject:

Re: PoddWatt EL84 Push-Pull Stereo Tube Amp - Support Thread

Hi, Thanks for the kind words. These amps really surprised me with the quality of sound. Your voltages are within the usual range so all should be well. Edcor now make the trannies with end bells and leads (we asked for them). Cute little devils - a few $$ more, but certainly worth it. The K40Y9s are from ebay sources. The Auricap is excellent as well. I really have not been able to tell which one I like better. I may depend on the phase of the moon or something. I have used both. The PoddWatt that is in my office uses the Sovtek 5751 and EH EL84s. I have some Mullards and Sovtek EL84 s to try when I get a chance. I have used the podwatt on my Martin Logan ESLs and it really sounds great, the modest output power is enough to get pretty loud in listening room.

On the 832s. I built a push-pull parallel U/L class A amp with some. I was rather disappointed with it. Bottom end was not strong and it just didn't sound very good. When I ran my usual battery of tests on it they were not too bad, just didn't sound nearly as good as the Odd Blocks and PoddWatt.

Good listeningBruce

Author:

MTron [ 19 May 2010, 00:15 ]

Post subject:

ECL85 (6F5P ) oddwatt clone

sampleaccurate wrote:

The initial ECL85 (6F5P) schematic "stolen" from Bruce:

So what values did you end up with using for the resistors you inserted into the circuit? I am also working on an amp, and my OT has no UL taps on it either....already have the OT, so i kind of want to just make it work

Author:

azazello [ 19 May 2010, 07:03 ]

Post subject:

Re: ECL85 (6F5P ) oddwatt clone

300-500 ohm.

Author:

MTron [ 19 May 2010, 08:20 ]

Post subject:

Re: ECL85 (6F5P ) oddwatt clone

OK. But just to be on the safe side, ill be a little more specific then i was with my last post at 2am...lol

Im building a very similar amp, the circuit for the most part is exactly the same, a notable difference is that i am using EL84 tubes (6BQ5)

I just want to make sure that a 300-500 ohm resistor is the proper one to use to adapt the design on that site to the one sampleaccurate modified, because i have read bits and pieces around that mention a 100ohm resistor

Im a total newb at this, i believe this is whats called "triode strapping"

Author:

azazello [ 19 May 2010, 09:50 ]

Post subject:

Re: ECL85 (6F5P ) oddwatt clone

Yes, this is triode mode oh output tubes!You can put double 3 pos. switch /for R and L ch./ for switching from triode to penthode mode....second end of 300 ohmto switch or to the plate, or to B+/200-300v/....... and compare both sounds!UL mode mix power of penthode and quality of the sound of triode modes!

Author:

MTron [ 19 May 2010, 10:53 ]

Post subject:

Re: ECL85 (6F5P ) oddwatt clone

Sorry, just to clarify

Wiring up the switch is no problem, i have lots of experience with electrical circuits, just not amp's

For the triode strap, use a roughly (to taste i assume) 300 ohm resistor to connect the screen lead (pin 9) to the lead coming from pin 7, which goes to the primary winding of the OPT

For full pentode mode, i run pin 9 (from each EL84 tube) directly to the center tap of the OPT? or is the 300ohm resistor also in series in this config as well??

Author:

sampleaccurate [ 19 May 2010, 11:06 ]

Post subject:

Re: ECL85 (6F5P ) oddwatt clone

MTron wrote:

OK. But just to be on the safe side, ill be a little more specific then i was with my last post at 2am...lol

Im building a very similar amp, the circuit for the most part is exactly the same, a notable difference is that i am using EL84 tubes (6BQ5)

I just want to make sure that a 300-500 ohm resistor is the proper one to use to adapt the design on that site to the one sampleaccurate modified, because i have read bits and pieces around that mention a 100ohm resistor

Im a total newb at this, i believe this is whats called "triode strapping"

I didn't see that thread. We're basically doing the same thing only I'm trying to do it with a Russian 6F5P equivalent of the ECL85 triode/pentode to eliminate the 5751 tubes. I'll be following your build since you'll almost surely finish before I do - I have too many projects going at once, but I finish everyhting eventually. I hope it works out well for you. If yours does and mine doesn't I might change my design to use different tubes.

Author:

azazello [ 19 May 2010, 11:37 ]

Post subject:

Re: ECL85 (6F5P ) oddwatt clone

Of course with 300 ohm in both cases!!/first end of res. is conn. to grid/. /sorry, I explaned not clarity/.